Apparatus for well surveying



April 6? 1937. G.` STRAATMAN 2,076,211

\ APPARATUS FOR WELL-SURVEYING Filed Jan. V25, 1955 'Patented Apr. 6, 1937 Alphons Gerard Hubert Straatman, The Hague, Netherlands, -assignor to Shell Development Company, San Francisco, Calif., a corporation of ,Delaware Y Application January 23, 1935, Serial No. 3,193

In the Netherlands January 25, 1934 Claims. (Cl. 73-32) This invention pertains to apparatus for determining the nature, thickness, dip and/or sequence of various geological strata by means of tempera- A ture measurements taken at various levels in a 5 well traversing said strata.

It hat been known to secure data on the geological formations'by studying and measuring the outcrops oiv strata appearing on the surface, or

by keeping an accurate record of the types of strata found at different depths in a number of wells drilled in the same field. In connection with similar investigations, the electrical proper-v tiesof `the strata have lately also been utilized. It is the purpose of this invention to provide `a new apparatus for obtaining data on thermal properties of subsurface strata. `These properties may here be summed'under the term of heat conductivity, which term, however, is not limited to thel 'conception known in physicsas the heat zovconductivity coefcient, but' embraces the whole complex of properties determining the rate at which a local temperature disturbance in a bore hole is neutralized by means of heat conducted to or-from adjacent earth layers. This complex thus comprises not only the conductivity coeflcient", but also such properties Vas specific heat, specific density, particular composition', etc.,

of the various strata. ,i

In practicing this invention, a disturbance is created in thetemperature field surrounding a v bore hole. This may be achieved, during normal drilling operations by means of the mudilushv circulating in the borehole, or by filling the borehole i witha liquid introduced for that purpose, such as water, petroleum, or a mixture of these liquids, said liquid or liquids diiering in temperature from the surrounding stratao Since it is known that the temperature of the subsurface strata increases with the depth, the temperature of the liquid should preferably be selected so as to lie outside the whole range of temperature prevailing in thetraversed strata, being kept above or,

as has been found more practicable, below said range. This liquid should preferably be of a sufy ciently high viscosity to prevent heat exchange throughv convection between vertical sections of the liquid columnA lling the well.

.At the levels corresponding to the various strata, heat willnow be lconducted to or. fromv these strata, so that the temperature offthe liquid will gradually approach7 the temperature of the strata, this process taking place at a greater or lesser speed dependent on the temperature dif; ference between the liquid and a given layer and 55 on the heat conductivity of this layer. Owing to 'tom of the well,- whilst the actual temperatures the diierence in heat conductivity of the various layers, the curve obtained from temperature readings will show irregularities, sinceV the temperature of the liquid at the level of a layer with a high heat conductivity will sooner approximate .the nal temperature than at the level of a layer vwith a low heat conductivity. Consequently, the

irregularities in the temperature curve will suplply information with'regard to the heat conductivity and, therefore, to the nature of the zvarious strata passed through. Particularly, if

several wells have beendrilled in the same field,

conclusions may be drawn in regard to the dip of the strata by determining the level of corresponding irregularities in these wells, without 15,

having to consider the nature of the strata. y

The diierences in heat conductivity of the various strata would be expressed most distinctly, if

it 'were possible to determine at any depth the difference between the temperature actually prevailing there, and the temperature which would prevail if all the strata had the same average vheat conductivity. The latter temperatures would show a gradual r-ise from the surface to the botwould deviate from the curve obtained to one or 25 to the other side according to the higher or lower heat conductivities of the strata traversed. Although it is, of course, impossible to record or construct a temperature curve based on an. average heat conductivity of the strata, such a 30 curve may be approximated by measuring the temperature of a thermally stable body, said body being lowered slowly, but at a uniform rate from the surface to the bottom of the well, or raised from its bottom tothe surface. With such movement, the body,l owing to its high heat-.capacity and/or its insulation, which may be provided, if desirable, will be unable to follow, the smaller temperature fluctuations, but its temperature will gradually rise or drop as the depth to which it is moved increases 'or decreases.-A If the body is lowered into the Well andatthe beginning of the vmovement the temperature of the body is the same as that of the surroundings, then its temperature during the movement will always be slightly lower thanv thev temperature according to the theoretical curve mentioned above. On the other hand, on the body being raised, its temperature will always slightly exceed that of the borehole and the other for the uid through which the body. passes; in addition, automatic means are provided for registering the diierence between' the temperatures to which said tem- 5 perature responsive means are simultaneously subjected. The heat responsive means are preferably provided in the form of thermo-couples as will be seen below.

A preferred form of apparatus suitable for the purposes ofthis invention will be better understood from the following description taken with reference to the appended drawing.

Figure 1 shows diagrammatically and partly in cross-section a. view of the device to be lowered into the well.

Figure 2 shows diagrammatically the connections of the thermo-couple and of the measuring equipment.

Referring to Fig. 1, a casing I, adapted to be lowered into the well by means of a cable, contains a central columnar body 2 extending below the casing into a column 3. In^the particular type of device represented in the drawing, the

heat-containing body described above is embodied in a number of bars 4, placed around the columnar body 2, and made of a metal such as copper, bronze, iron, lead, etc., or of any other adequate material. It should, however, be understood that this invention is not limited to any particular shape or location of the parts 4, which l may be varied at the will of the designer. 'Ihe bars 4 are electrically insulated from each other and havea relatively high heat capacity. They are, moreover, protected by the casing l from a direct contact with the liquid of the well. The

bars d are connected in series by wires 5 arranged in pairs and made of different materials to provide@ thermo-couple effect, the junctions 6 of said wires being exposed to the temperature 40 of the well, while the junctions 9 are, as obvious, at the temperature of the bars 4, which form the body of relatively large heat capacity referred to hereinbefore. The junctions l` may be suitably protected from damage, but in such a manner as to allow them to acquire practically immediately the temperature ofthe surrounding liquid.

The first and the last of the bars 4 connected in From the above, it is clear that the method of 1 this invention may be carried out in operation as follows:

As soon as the circulation of the mudiflush is stopped and the liquid in the well comes to a standstill, this liquid will take or giveoi a' cer-Y tain quantity of heat from or to its surroundings,

if a dierence in temperature exists between them. The amount of heat transferred depends on this temperature dierence and on the heat conductivity of the strata at diierent levels. When the apparatus of Fig. 1 is slowly lowered into the well, the difference inv temperature between thev elements 4 and tlfe well uid at various levels corresponding to strata with diierent heat conductivitieswill be translated through the thermocouple eii'ect, into differences of potential registered by'potentiometer 8. By carefully recording the readings of the latter, it is possible to plot the temperature differences against the depth so that the curve obtained will give -information as to the particular strata traversed by the well.

Furthermore, by comparing in some cases such a curve with similar curves obtained from other wells in the same eld, it becomes possible to determine the general geological structure .of the field and to establish correctly for example on what portion of an anticlinical structure the well is located.

I claimv as my invention:

l. An apparatus for surveying subsurface strata traversed by a. borehole comprising a metallic element of relatively large heat capacity capable of being lowered into a borehole and of following the general temperature trend of the boreholev iluid, means associated with said element and responsive to a diiference in temperature between said element and the well liquid surrounding said element, and means coopcratir:d with said tem-- perature responsive means adapted to register said temperature diierence. l

2. An apparatus for surveying subsurface strata traversed by-a borehole ycomprising a metallic element capable of being lowered into the borehole and of following the general temperature trend of theborehole liquid, a thermocouple associated with said element and having one of its junctions at the temperature of said element and the other junction exposed to the liquid in the borehole, and means connected to said thermocouple for indicating the resulting voltage thereof.

3. The apparatus of claini 2 wherein the metallic element is made an effective part of the thermocouple.

4. An apparatus for surveying subsurface strata traversed by a borehole, comprising a metallic body of relatiyely large heat capacity capable of being lowered into the liquid lling a borehole and offollowing thegeneral temperature trend of the borehole liquid, and consisting of several metal elements electrically insulated from each other, thermocouple -connections between said elements vforming two series of thermocouple junctions, one series being at the temperature of said body and the other at the temperature of the liquid in the borehole, and means connected with said thermocouple connections for indicating the resulting voltage thereof.

' l5. An apparatus for surveying subsurface strata. traversed by a borehole comprising an element of relatively large heat capacity capable of being lowered into a borehole and offollowing the general temperature trend of the borehole fluid,

. means associateda with said element and respon- 

